Linear stages are widely utilized for ultra precision manufacturing in industries of optical electronics, semiconductor and mechanics. A linear stage includes a first moving stage configured to move in a first moving direction, and a second moving stage configured to move in a second moving direction. Ideally, the first and second moving directions are perpendicular to each other. However, several kinds of errors exist in reality so perpendicularity cannot be ensured, thereby hindering promotion of precision in manufacturing.
Conventional measurement devices like those disclosed in Taiwanese Patent Nos. I345878 and I320688 are implemented by a plurality of light sources and a plurality of sensors to emit incident light beams to the linear stage, to receive reflection light beams resulting from reflection of the incident light beams by the linear stage, and to determine errors associated with the linear stage. However, since multiples sets of light sources and sensors are required, a higher cost and greater complexity of implementation of the above-mentioned conventional measurement devices may be inevitable.